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    <script>
        // 使用for循环 - 求出数组元素的和[5, 8, 9, 2, 1, 5]
        let arr = [5, 8, 9, 2, 1, 5]
        let a = 0
        for (let i = 0; i < arr.length; i++) {
            a += arr[i]
        }
        console.log(a);
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